The present invention relates to call tariff determination in mobile telecommunication networks and more particularly to the determination of call tariffs for provision to an access network in respect of a mobile telephone subscriber.
In today""s competitive mobile telephone market, in order to attract new customers, operators are operating a diverse range of payment options. In addition to the conventional payment scheme where a subscriber is billed regularly for telephone calls made over a period immediately preceding the issuing of a bill, there is for example the prepaid card schemes where a user purchases a card and then uses a secret number provided on the card to top-up an account maintained by his operator. The user is able to make and receive calls until such time as the balance in his account falls to zero. The account must be topped-up using a new prepaid card before the user can make and receive calls once more. Many new services are also being introduced by mobile telephone operators to attract new customers as well as to maintain their existing customer base. One such service, which is in limited current use, is known as xe2x80x9cAdvice of Chargexe2x80x9d and allows mobile telephone""s to be provided with call charge information during the call set-up phase to enable call charges to be computed by the telephone either during or after a call.
In a typical GSM/GPRS mobile telecommunications network, there is present a rating node or Charging Control Node (CCN) which maintains details of the tariffs charged by the operator for the complete range of call options (e.g. home mobile telephone to home mobile telephone, home mobile telephone to other national telephones, international tariffs, etc), and which implements a Service Control Function (SCF). The SCF of the CCN may communicate with a Service Switching Function (SSF) associated with the Mobile Switching Centre (MSC) serving a Mobile Station, in order to transfer tariff determining information in one direction (i.e. from the MSC/SSF to the CCN) and determined tariffs in the other direction.
Providing that a subscriber""s telephone is registered with his home network, there is in principle no bar to providing services such as Advice of Charge and to controlling and monitoring in real time prepaid card subscribers and the like, as all the necessary information is available at the home network""s CCN (or can be readily obtained by that node). Problems arise however when a mobile telephone subscriber is not at home but rather is registered with some foreign mobile telephone network (the term xe2x80x9caccessxe2x80x9dnetwork is used below to describe the network to which a subscriber is directly connected).
Such a foreign access network should be able to determine real time charging information for a roaming subscriber if prepaid subscribers are to be allowed to roam, or if services such as Advice of Charge are to be available to roaming subscribers. Indeed this may be necessary whenever subscribers have a credit ceiling that must not be exceeded. However, the foreign network SSF does not necessarily know the call tariff to be applied by the subscriber""s home network nor does the home network necessarily know the tariff to be applied by the foreign network (it is the home network which has overall control of billing operations for its own subscribers). It is not realistic to expect every charging node in every network to be provided with a comprehensive list of caller tariffs applied by other network operators, as tariffs quickly become outdated and/or operators are not be willing to provide their own call tariffs to their competitors.
One solution to the above problem which has been proposed is to provide every network with one or more so-called xe2x80x9crating nodesxe2x80x9d (for example Service Control Functions) which knows the tariffs of the network to which they belong. When a roaming subscriber initiates a call using a foreign network as the access network, the responsible SSF of the access network contacts a rating node of the subscriber""s home network to obtain the home network""s tariff for the call in question. This tariff is then returned to the SSF of the access network to enable it to calculate real time charging data.
A limitation of this proposed solution is that the rating node of the subscriber""s home network does not know the tariff that the foreign network will apply to the call (this information is only provided to the home network after termination of the call). Thus, the real time charging information generated at the SSF of the foreign network will be an estimate, based only upon the tariff of the home network and will not correspond to the actual tariff applied to the call (and upon which the subscriber""s telephone bill will be based).
It is an objective of the present invention to overcome or at least mitigate the above noted disadvantages of existing and currently proposed solution of providing a real time or near real time call charging information to a foreign network which is acting as an access network for a roaming mobile subscriber.
According to a first aspect of the present invention there is provided a method of determining a total call tariff in respect of a call from a Mobile Station currently registered with a foreign network, the method comprising the steps of:
sending a total call tariff request from a charging function of the foreign network to a rating node of the mobile telephone subscriber""s home network, said message including a call tariff portion of the foreign network;
at the rating node, determining said total call tariff on the basis of the foreign network tariff portion and a call tariff or charge factor of the home network; and
returning the determined total call tariff to the charging function of the foreign network.
Embodiments of the present invention provide a relatively easy and straightforward way of providing total call tariff information to a foreign network, which information represents the true tariff to be used by a subscriber""s home network. In these embodiments, the home network retains control of the charging operation and furthermore there is no need for the home network to disclose complete details of its charging formula to the foreign network.
Preferably, the rating node applies a multiplier to the received foreign network""s tariff portion in order to determine the total tariff.
Preferably, the sending of said total call tariff request from the charging function of the foreign network is triggered by receipt at the foreign network of an Address Complete Message (ACM) which is a response to the initiation of a call by the Mobile Station. The sending of subsequent call tariff requests may be triggered by receipt at the foreign network of external charging information. More preferably, the determined call tariff is available at the charging function of the foreign network when an Answer Message (ANM) is received at the foreign network.
Preferably, the charging function of the foreign network is a Service Switching Function (SSF). The SSF may be a stand-alone node, or may be co-located with an MSC of the foreign network. Preferably, the rating node of the home network is a Charging Control Node.
More preferably, said ACM and ANM are received by the serving VMSC/SSF.
Preferably, the method of the present invention is implemented using the CAMEL mechanism and the CAMEL Application Part (CAP) protocol.
The present invention is applicable in particular to GSM telecommunications networks, both in respect of circuit switched and packet switched calls. The invention is also applicable to other telecommunications systems including UMTS.
Preferably, said call tariff portion of the foreign network relates in whole or in part to network based number translation services. Preferably, said call tariff or charge factor of the home network relates to subscribed services, subscribed dialled services, and/or charging services.
According to a second aspect of the present invention there is provided apparatus for determining a total call tariff in respect of a call from a mobile telephone subscriber currently registered with a foreign network, the apparatus comprising means for sending a total call tariff request from a charging function of the foreign network to a rating node of the mobile telephone subscriber""s home network, the message including a call tariff portion of the foreign network, means for determining at a rating node of the home network the total call tariff on the basis of the received foreign network""s tariff portion and a call tariff or charge factor of the home network, and means for returning said total call tariff to the charging function of the foreign network.